Fail-safe speed control system for railroad trains

ABSTRACT

An improved fail-safe speed control system for railroad trains in which the traffic conditions which establish the permissible speed for a train are determined at a central station in accordance with track occupancy indications transmitted from wayside locations. These indications and return speed command signals are carried over a communication system linking the central station and all wayside locations. To eliminate possible incorrect delivery of proceed speed commands due to communication system faults, restricted speed commands are delivered to wayside locations over direct connections from the central station completed in response to occupied track indications. For additional safety, an occupied track indication is cleared only when an indication is recorded that the corresponding train has moved into the advance track section.

United States Patent [72] inventor Philip R. Schatzel OTHER REFERENCES shill" Township, Allegheny County, W. P. Bollinger, Welco Working on BARTD Signaling, Dec. PP 764,524 1967 Railway Signaling and Communication pages 18- Had 1968 23. (The office copy of this article was supplied by the applif June I971 cant. it is therefore not considered necessary to send applicant Asslgnee wesfinghou" Brake cmnp'ny a copy of the article with this office action) Swissvale, Pa.

Primary Examiner-Arthur L. La Point Assistant Examiner-George H. Libman AttameysW. L. Stout and Arba G. Williamson s4] FAIL-SAFE SPEED CONTROL SYSTEM FOR 8 "P fail'safe F. System RAILROAD TRAINS railroad tra ns in which the traffic conditions WhlCh establish the pennlssible speed for a tram are determined at a central 4 Claims, 2 Drawing Figs.

station in accordance with track occupancy indications trans- [52] US. Cl 246/34CT, min d from way ide locations These indications and return /63C speed command signals are carried over a communication [51] Int. Cl. B611 23/20 system linking the central station and all wayside locations. To [50] Field of Search 340/ 163; li inate ssible incorrect delivery of proceed speed com- 63 137 mands due to communication system faults, restricted speed 56 R f Ci ed commands are delivered to wayside locations over direct conl e fences nections from the central station completed in response to oc- UNITED STATES PATENTS cupied track indications. For additional safety, an occupied 3,328,581 6/1967 Staples 246/37 track indication is cleared only when an indication is recorded 3,268,727 8/1966 Shepard 246/ l 87 that the corresponding train has moved into the advance track 3,359,416 12/1961 Wilcox 246/34 section.

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Truly/7166601 Lam/mzm/ L029. 7 Faced/er fn/bzmafzbzz Ldrze PATENTED JUN 1 197:

SHEET 1 BF 2 PATENTED JUN 1 9n SHEETZUFZ" Q R b g k QANMX mg mil 'Ul QED @Qsw SE FAllL-SAll lE fiillilEE CONTROL @YSTEM lFOllR RAILROAD TllifisilNS This invention relates to an improved fail-safe speed control system for railroad trains. More particularly, my invention lies in additional fail-safe provisions for a railroad speed control system which centralizes much of the apparatus for train detection, traffic safety criteria development, and speed control selection.

The development of automatic train operation systems (ATO) has required new approaches in the design of railway signaling and speed control arrangements, especially for rail rapid transit systems. For example, in such ATO rapid transit systems, the supervisory control from a central headquarters which is normally incorporated into the ATO requires subordinate centralized locations where train operation can be influenced. A primary means of influencing train operation is through the control of the operating speed. For example, if a following train has been delayed, the preceding train may be slowed to adjust the average headway between the trains or may be held at a station stop for a slightly longer period. Conversely, station stops of a following train may be shortened in order to reduce lost headway. The operating speed of trains is also involved in safe operation of any such transit system. This is separate and distinct from the supervisory control. Speed control systems for railroad trains are known in the art but are not always easily adaptable to supervisory control without extensive modification. However, whatever other requirements may exist, a completely fail-safe operation of the speed control system must be maintained with absolute certainty.

One proposed modification of speed control systems to adapt to ATO with supervisory control is the use of centralized equipment stations along the stretch of track. Train detection indications are then transferred to the central stations from the wayside detectors. Vital safety checks are made using these track occupancy indications received from the actual wayside locations and recorded by occupancy indicator means at the central station. Speed controls are then selected in accordance with the developed safety criteria and are transmitted back to the wayside locations for further transmittal to the trains. Supervisory control, that is, control between the headquarters and these centralized stations, is then exercised by modifying the selected speed control signals within the safety factors for the particular track section. Communication between wayside and central station is provided by a communication system of any known type which will provide the functional operation desired. The problem then becomes one of maintaining the high fail-safe level required in railroad operation when automatic signaling and speed control systems are in use. An added source of possible trouble or error is the transmission arrangement between the wayside detectors and speed control devices and the central equipment station since all communication systems are subject to some errors in transmission due to external causes. A design requirement is thus added that such communication system errors must not result in any improper or incorrect speed control signals.

Accordingly, an object of my invention is an improved failsafe speed control system for railroad trains.

Another object of the invention is an improved fail-safe arrangement for railroad speed control systems in which the speed selections for a stretch of track are centralized at a single location.

Still another object of my invention is the provision of an arrangement of circuits and apparatus to prevent delivery of incorrect speed command or control signals to a train from a central equipment station due to communication system transmission faults.

A further object of my invention is a circuit arrangement for use in speed control systems for a stretch of railroad track which augments the communication channels between a central equipment station and associated wayside locations in order to prevent the incorrect delivery to a train of a proceed speed command when traffic conditions in advance require a restricted speed.

lt is also an object of the invention to add an arrangement to railroad speed control systems which will check the correct delivery of track occupancy indications to a central equipment station at which train speed selections are determined.

It is a further object of this invention to augment the regular communication channels in order to assure delivery of a restricting signal to trains in a railroad speed control system in which speed selections are made at a central location.

Still a further object of my invention is an arrangement for use in railroad signaling and speed control systems with centralized traffic recording and speed selection which prevents a following train from receiving a proceed speed command due to transmission faults occurring in the communication system between the wayside locations and the central station.

Other objects, features, and advantages of my invention will become apparent from the following specification when taken with the appended claims and accompanying drawings.

Broadly speaking, the arrangement of my invention is added to a basic railroad speed control system in which a stretch of track is divided into a series of track sections, each section being provided with a audiofrequency (AF) track circuit for train detection. Each wayside location, that is, each point of division between adjoining sections, is provided with a track transmitter and a track receiver unit. The transmitter is coupled to the rails of the stretch in order to transmit audiofrequency current toward the next location in advance, that is, through the advance track section rails. The receiver is also coupled to the rails to receive audiofrequency current from the transmitter at the first approach location, such current flowing through the approach section rails. The terms approach and advance, as used herein, are defined in the conventional manner well ltnown in railway signaling art. Briefly, an approach section is that section of track through which a train moves as it approaches the location of the observer or apparatus under discussion. Conversely, an advance section of track is that section through which a train moves, or into which it moves, after it has passed the observer or apparatus.

In the basic arrangement, the track transmitters at adjacent locations supply current of different and distinct audiofrequencies to the track, a specific rotation of three different sets of frequencies being used. This allows elimination of insulated joints between sections since there will be no interference between currents of different frequencies flowing in the rails of adjoining sections. Obviously, the receivers are separately tuned to the same sets of frequencies, a particular receiver being tuned to respond only to the current flowing through the approach track section from the transmitter at the approach location. Each track transmitter is so coupled to the rails, however, as to also transmit its AF signal current into the approach track section as well; thus the need for three sets of frequencies to assure noninterference between rail currents. The output of each transmitter is selectively modulated, on a. frequency shift basis, so as to provide speed control signals to trains approaching its location. Such trains, of course, must be provided with apparatus responsive to track currents of all frequencies used in order to detect and demodulate the speed command signals to effect a speed control upon the train. it should be noted that the train detection signal or current flowing in the advance track section from each track transmitter is, of course, also modulated in the same pattern.

In modifying the more conventional prior art systems, the basic system here moves the selection of the speed commands transmitted by each wayside track transmitter to a central equipment station located at one point along the stretch of track. The specific selection for each track transmitter is then transferred to the corresponding wayside location. Under this arrangement, the determination or development of the safety criteria or traffic conditions on which the speed selection is based must also occur at this same central station. This is true since the existing advance traffic and/or safety conditions establish the speed at which a particular train may be permitted to move. The determination of the traffic safety criteria requires that indications of the positions of the various trains be available. Therefore, the train detection indications must be transmitted to this central station. Thus the basic system provides a communication system between the central equipment station and each wayside location. Although other types may also be used, the system is herein described as a multiplex code system operating in a continuous scanning manner.

Transmissions between the central station and each wayside location are repeated during each cycle of scanning operation. In other words, train detection indications are transmitted in from the wayside locations to the central station while speed command controls are transmitted out from the central station to each wayside location. Location selection, therefore, must be and is provided on a one-at-a-time basis.

Further provided at the central station for each track section along the stretch are a speed command generator, a speed command comparison unit, and a vital safety protection unit. A speed command generator transmits a selected speed command signal to the wayside track transmitter at the entrance of the corresponding section. Each speed command comparison unit receives the track occupancy indications from the receiver located at the exit end of the corresponding track section. This track occupancy indication may also include an indication of the actual received speed command since, as previously indicated each track transmitter transmits the same modulated AF current in both directions from its location. Such speed command signals, of course, are received by a particular receiver only when the approach section, that is, the section at whose exit end the receiver is located, is not occupied by a train. At the central station, the speed command selection transmitted from the corresponding generator is compared with the received indication to determine that proper delivery of the selected speed command has occurred. The vital safety protection unit receives track occupancy indications from the corresponding comparison unit. Effectively, this is the track occupancy indication from the field. However, an indication that the corresponding section is not occupied can be supplied to the safety unit only if the speed command comparison reveals identical speed command signals. If such a comparison is not present, then a track occupied signal is provided by the comparison unit to the associated safety unit regardless of the received information. The safety unit records its own track section occupancy and checks the occupancy of sections in advance through interconnections with the safety units corresponding to such sections. In this manner, the advance traffic conditions and thus the safety criteria for an approaching train may be determined. The safety unit arrangement than selects an appropriate speed command for such an approaching train and delivers an indication of this selection to the associated speed command generator. This latter unit transmits the proper command signal to the wayside track transmitter at the entrance end of the corresponding section. This track transmitter, of course, feeds its modulated signal in both directions and particularly towards a train in the approach section to provide speed control for that train.

When a train is occupying the section corresponding to a vital safety protection unit, no comparison, of course, is possible between the selected speed command signal transmitted to the entrance end wayside location and the indication received from the exit end of the section since the train shunt in the track section blocks the reception of any signal by the receiver at the exit end. Thus no check is made, under these conditions, on the proper delivery of the selected speed control command to the corresponding wayside track transmitter for delivery to a following train in the approach section, such signal being a restricted speed command. In order to overcome the possibility of a fault in the communication system causing the delivery of an improper proceed signal to this folsafety unit, to provide the restricted speed command direct from the associated speed command generator. This assures that a proper restricted speed signal will be delivered to the rails for transmittal to a following train under all conditions of communication.

My invention also adds a special pickup circuit for the track relay within each vital safety protection unit which checks the release of the advance section track relay. Normally, each track relay is held energized by a stick circuit so that, after releasing when its corresponding track section is occupied by a train, it can only pick up when the train has moved into the advance track section to cause the release of that track relay. This arrangement assures that an error in the communication system in delivering track occupancy indications to the central station can not, through improper selection of locations, in' correctly cause the pickup ofa track relay to indicate a nonoccupied section where, in actuality, the section is still occupied by a train. Rather, only when that train has moved forward into the advance section and such occupancy has been recorded can a particular track relay receive energy to again indicate or record the nonoccupied condition of its section.

I shall now describe in more detail the system of my invention with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of the wayside apparatus at several locations of a railroad speed control system embodying the arrangement of my invention.

FIG. 2 is a similar diagrammatic illustration of the associated apparatus at the central equipment station in the speed control system embodying my invention, which centralized apparatus cooperates with the wayside apparatus to effect the speed control of trains moving through the stretch of track.

In each of the figures of the drawings corresponding parts of the apparatus are designated by similar reference characters. Conventional block diagrams are used to designate apparatus whose details are not involved in the specific arrangement added to the system by my invention. The apparatus designated by these conventional blocks may be selected from several types known and available in the art which will provide the operation of the basic system involved.

Reference is now made to FIG. 1 for the following description of the wayside apparatus of the system embodying my invention. Across the top of FIG. 1 is shown a stretch of railroad track, each rail designated by a conventional single line symbol. This stretch of track is shown divided into various track sections, designated by the reference AT, BT, CT, and DT, which provide examples of the sections which would exist through the entire stretch. In the following description, each division point between such track sections is defined as a wayside location. Such locations are actually established by crossbond connections between the rails, each designated by the reference CB with a suffix numeral the same as the location number. Thus, between track sections AT and BT, a crossbond CBI marks the division point which becomes then wayside location 1.

Each wayside location is equipped with a track transmitter and a track receiver, each with its own assigned set of frequencies. These units are illustrated by conventional blocks since the details are not involved in my invention, each block being designated in accordance with the function of the apparatus and with the specific assigned frequencies. In each case, the frequency set is indicated by a combination of two related frequencies such as, for example, in the transmitter at location I where the frequencies are designated as fl and fl. This designation of the assigned frequency is used since, in the basic system, the output of each track transmitter is frequency shift modulated to provide a selected pattern of the output frequencies. The transmitters and receivers at each location are coupled to the rails. The transmitter coupling is through the illustrated loop which is parallel to the rails in each adjoining section at that location. Thus the transmitter output signal is induced into the rails of each section and flows both ways from the location into the approach and advance track sections. The receivers are coupled through a transformer action, the illustrated coils normally being part of an impedance bond which includes the crossbond connection CB at the location.

As previously indicated, each track transmitter is capable of providing an output of two related frequencies by frequency shift operation. The output frequency pattern is controlled by the associated frequency shift modulator which in each case is shown by a conventional block since the details of the circuit arrangements are not critical to my invention. The pattern selection is actually supplied from a speed command memory unit which is a storage unit receiving the speed command selection from the central station over the communication stem in use, as will be shortly described. The memory unit is likewise shown by conventional block as any of several well known types may be used in the arrangement. The track receiver at each location is also tuned to a specific set of frequencies, not that of the associated track transmitter, but rather the same frequency set as that of the approach location track transmitter. For example, it will be noted in FIG. I that the transmitters at locations 1 and 2 correspond in frequency to the receivers at locations 2 and 3, respectively. The transmitter at location 3 feeds the similarly tuned receiver at the next location t, to the right of FIG. 1, in advance along the stretch of track, The receiver at location l is tuned to receive energy from the track transmitter at the entrance end of track section AT which, since three different and distinct frequency sets are used in rotation, is assigned the same frequency set as the track transmitter at location 3. As previously mentioned, by this rotation of three frequencies, interference between the rail currents in the adjoining track sections is avoided, even though each track transmitter transmits in both directions from its location, without the use of insulated joints, the crossbond connections CB aiding in this operation.

A communication system is obviously required between the several wayside locations and the central station. This communication system is illustrated across the bottom of F108. 1 and 2 by single line convention as comprising three channels which extend between the central station of FIG. 2 and all locations, three of which are illustrated as examples in FIG. 1. Preferably, this communication system is a multiplex type code control system which provides continuous scanning of all of the wayside locations through repeated cycles of operation. To this end, synchronizing pulses must be provided and are specifically shown as supplied over the upper channel, of the three illustrated, designated as the synchronizing pulse line. These pulses provide location selection between the several locations for transmission and reception. Each location is provided with a time slot selector, shown by a conventional lefthand since such selection units are known in the art, These conventional locks are distinguished only by a numerical designation which corresponds to the location number. Each time slot selector counts the synchronizing pulses from the beginning of each cycle of operation and provides an output pulse when a preset number of such pulses, distinctive to that location, have been counted during a particular cycle. This output pulse is used to enable or actuate the various gate circuits at that location which are also shown by conventional blocks since such circuitry is well known. When a gate is enabled, it connects the associated location apparatus to the communication system. Specifically the enabling of the left-hand gate shown at each location connects the transmitter apparatus group, more specifically and directly the speed command memory unit, to receive speed command signals over the transmitter command line from the central station. At the same time, the enabling of the other gate at each location connects the wayside track receiver, through a line driver which provides sufficient energy, to the communication system and specifically to the receiver information line over which the track occupancy indications are transmitted to the central station. The similar enabling of gates at the central station will be discussed shortly when that apparatus is described hereinafter.

The receiver units at each location, in addition to receiving a track current signal, are also capable of developing an indication signal for transmission to the central station at any time that the associated gate is enabled by a time slot pulse. The indication signals transmitted to this central station basically indicate whether or not that particular receiver unit is receiving a signal from the associated transmitter at the entrance end of that section. Obviously when a train is occupying a particular section, its wheel and axle units shunt the track current between the rails so that no signal is received by the track receiver at the exit end of that particular section through its coupling with the rail circuit. For example, when a train is occupying section ET, the track current supplied by the transmitter at the entrance end is shunted away from receiverfl-f l at the exit end which thus receives no signal through its coupling with the track rails. Receivers fl-jl then generates a signal for transmission to the central station, when its gate is enabled, indicating that no signal is being received and that the corresponding track section is therefore occupied by a train. When no train is occupying section BT, receiverfl-fl does receive current rough its coupling with the rails and generates an indication that the track section is not occupied. However, since the track transmitter signal induced in the rails is the same in each direction from a particular location, each track receiver also receives, when the signal is not shunted, the speed command signal being carried by the use current. Each receiver unit is designed to develop a supplemental indication of the speed command signal received which is also transmitted to the central station for purposes which will be discussed shortly. Any track not-occupied indication, therefore, has combined therewith an indication of the speed command signal supplied to a train in the approach section. The actual output of a track receiver unit, when the gate is enabled, is applied through a driver unit, shown by conventional block, which provides sufficient output levels for the communication system operation, such use of driver units for amplification purposes being conventional. The output of the driver units is applied to the indication channel of the communication system, designated as the receiver information line, for transmission to the central station.

At each location, the track transmitter and its associated apparatus receive speed command signals from the central station through a conventionally shown connection to the transmitter command line. For purposes of the immediately following description, it is assumed that a direct connection, illustrated by the dotted connection bypassing the lettered terminals, exists at each location between the communication system and the transmitter group. When the proper gate at a wayside location is enabled by the associated time slot selector, that is, the location is selected, the existing speed command signal is delivered to the speed command memory unit for storage. This memory unit stores the received speed command for continued control of the associated modulator unit. Depending upon the specific communication system used, this speed command signal may be immediately delivered, or the stored speed commands at all wayside locations may be sim ultaneously delivered from the memory unit to the associated modulator unit at the end of each cycle of the scanning operation of the communication system. In any event, when the frequency shift modulator unit receives the speed command signal, it elects a modulation pattern in accordance with the received signal and controls the operation of the associated track transmitter. The output of the track transmitter, operating on the frequency shift principle, consists of a series of pulses varying between the two frequencies of the assigned set in the pattern determined by the speed command signal.

The transmitter output is induced into the rails through the loops previously discussed and causes current to flow in both directions in the track sections. Trains traveling over this stretch of track are provided with apparatus which is responsive to receive and to decode these modulation patterns of the various frequencies to obtain the speed command signals for control of the train speed. It is to be noted, of course, that once a train has passed over the cross bond connection CB at a particular location, the speed command signal being transmitted by that wayside track transmitter is no longer effective to control the train but rather the speed control of the train shifts to the next transmitter in advance, that is, at the exit end of that section into which the train has passed. In other words, transmitterfl-fl provides a speed control signal for trains approaching through track section AT but once a train has passed crossbond connection CB1, the speed control for that train as it occupies section BT shifts to the output of transmitterf2-f2' at the next location.

Referring now to FIG. 2, the central station apparatus shown therein is divided into groups in a roughly equivalent manner to that for each wayside location. Distinct from the other apparatus, however, is the synchronizing pulse generator shown conventionally in the lower left of P16. 2. This unit supplies, over the conventionally shown connection to the synchronizing pulse line, the synchronizing pulses which control the communication system operation. Also shown across the bottom of HO. 2 are time slot selector units, equivalent to those at the various wayside locations, which are used to enable gate circuitry which activates the corresponding groups of apparatus at this central station location. These time slot elector units at the office are identical in operation with those at the wayside locations and count the synchronizing pulses, each being preset to provide an output pulse at a preselected synchronizing pulse count different for each selector. Where the basic number of a time slot selector at the central station is identical with that at a wayside location, both are actuated to provide output pulses on the same numbered synchronizing pulse during each cycle of operation of the communication system.

The apparatus at the central station is associated into groups corresponding generally to the track sections rather than specifically to the wayside locations. However, in each group of central station apparatus are units which may be specifically associated with a particular wayside location. For example, a speed command generator unit SCG is provided for easy wayside location. These units, which are shown conventionally by blocks since the details are not specifically a part of my invention, originate and transmit the speed command signals to the wayside track transmitter. Since the output signals of a wayside track transmitter are effective for speed control only in the approach tract section, a suffix letter designating the track section which it controls is added to the general reference SCG for each speed command generator unit, e.g., unit SCGA is the central speed command source for selection AT. The actual speed command selection is supplied to each speed command generator from the vital safety protection unit VSP associated therewith, which units will be described shortly. This selection is designated by the information flow line shown between each safety unit and the associated speed command generator. For example, when time slot selector No. l is actuated, i.e., responds to the first synchronizing pulse of each scanning cycle, it provides an output pulse which enables the farthest left gate of those shown. This actuated gate completes the connection from speed command generator SCGA to the communication system, specifically to the conventionally shown transmitter command line. This speed command signal is transmitted over the communication system and received immediately through the simultaneously enabled gate at wayside location 1 by the speed command memory unit here located (at the left of FIG. 1).

Information transmitted from the various wayside track receiver units is received at the central station by the speed command comparison units shown conventionally by block diagram. In other words, when a particular gate is enabled to connect a speed command comparison unit with the receiver information line of the communication system, information from the then active, i.e., enabled, wayside track receiver is received by this comparison unit and recorded. It is to be noted that the comparison unit associated with each speed command generator is actually connected to receive indications when its associated gate is enabled by the next succeeding time lot selector unit. This operation is necessary since it is the transmitter and receiver units a the wayside locations at opposite ends of each track section that are associated in the train detection operation. In other words, although the speed command signal for transmitterfl-fl' at wayside location 1 is transmitted from the central station by speed command generator SCGA during the first time slot selection period, it is receiverfl-fl at location 2 which receives the track current generated by that transmitter for purposes of train detection. Since this particular track receiver is located at wayside location 2, its signal must be received by the speed command comparison unit for track section BT when time slot selection No. 2 is actuated.

When active, the comparison unit receives information regarding track occupancy, that is, whether or not a signal is being received by the corresponding wayside track receiver. This track occupied or nonoccupied indication is retained by the comparison unit for application to the associated safety unit during the period between the specific reception of such indications from the wayside units. These comparison units also receive from the corresponding wayside receivers the supplemental indication of the speed command signal actually received. This speed command indication is compared with that selected for transmission from the associated speed command generator as indicated by the information flow line shown between each associated set of speed command generator and speed command comparison unit. This comparison of the selected and received speed command signals is a partial safety check upon the proper delivery of the selected speed command signal to the corresponding wayside track transmitter. if the comparison fails, then a nonoccupied track indication otherwise received by the speed comparison unit is invalidated and an occupied track indication is instead supplied to the associated safety protection unit. Obviously, if the rack section is occupied by a train, no comparison is possible since the wayside track receiver under these conditions receives no signal. Of course, since the speed command comparison unit the receives a track occupied indication, such indication is supplied during this period to the safety protection unit.

The vital unit within each group of apparatus at the central station is the frequently mentioned vital safety protection unit. One such unit is provided for each section in the stretch of track involved. Each unit shown is herein designated by the reference VSP plus a letter suffix which corresponds to the distinguishing prefix of the corresponding rack section reference. For example, the vital safety protection unit VSPB for track section HT is shown in the upper left of FIG. 2 by a conventional block diagram, since much of the circuitry is conventional and not a specific part of my invention. These units VSP accomplish the safety checks of the traffic conditions existing throughout the stretch of track. Basically, each unit provides the safety check of advance traffic conditions for a train which will enter the corresponding track section. As previously indicated, each such safety unit receives train location information from the associated speed command comparison unit and also from adjoining section VSP units, as indicated by the two-way information flow arrow shown between adjacent safety protection units. Briefly and basically, each VSP unit receives from its associated speed command comparison unit information as to whether or not the corresponding track section is occupied by a train. Similarly, the information received from adjacent safety units is relative to whether or not trains are occupying the corresponding track sections.

It is herein assumed that the basic circuits in each vital safety protection unit are relay circuits equivalent to one of the conventional or well-known signal system long in use for railroad signaling arrangements. The use of such circuitry allows the use of vital or safety type relays, which have fail-safe characteristics, to assure complete and adequate safety of operation of trains moving throughout the section. If desired, solid state circuits replacing such relay circuitry may be used providing only that they have been designed to include failsafe characteristics at least equivalent to that provided by the available vital safety type railway signaling relays. This absolute failcsafe type of apparatus is required since the circuits within each VSP unit determine the traffic safety conditions and select the speed command signal for trains approaching the corresponding track section. This speed command selection is supplied, over the previously mentioned connection designated by a conventional information flow arrow, to the associated speed command generator for further transmission to the corresponding wayside location.

In order to illustrate the specific features of my invention, there is shown within each safety protection unit a track relay for the corresponding track section to record or indicate the track occupancy condition within that section. Each relay is designated by the reference TR with a letter prefix corresponding to that for the track section. For example, within unit VSPB is shown track relay BTR, which is the track relay or track section ET. The basic control for each track relay is from the associated speed command comparison unit in accordance with the track occupancy indication received from wayside location. In other words, energy is supplied from the speed command comparison unit, if the track section is not occupied, over connections indicated by the flow arrow from each comparison unit to the associated VSP unit and then over connections, shown partially by a dotted line, to the relay winding. When the track section is occupied, energy is removed from these circuit connections. The conventional dotted portion of these connections covers any intervening apparatus found necessary in a specific arrangement to provide sufficient energy or other safety checks prior to application of the received track occupancy indication to the track relay.

Normally, each track relay is held energized by a stick circuit which is added to the basic system by my invention. For example, the only circuit by which relay BTR normally receives energy from the associated speed command comparison unit includes the winding and front contact a of relay BTR. As long as a nonoccupied indication is periodically received from the wayside location, energy is supplied to this circuit and relay BTlR remains energized. Obviously, when an occupied track section indication is received by the comparison unit, energy is removed from this holding arrangement and relay BTR releases, opening its front contact a to interrupt the stick circuit. Each track relay is provided with a pickup circuit, in accordance with my invention, which includes a back contact of the track relay for the advance track section. For example, for relay BTR, the pickup circuit includes, in addition to the winding of relay BTR, back contact b of relay CTR in unit VSPC. This circuit is supplied with energy from c speed command comparison unit associated with unit VSPB when a nonoccupied indication is again received from the field location. Since the pickup circuit is not complete until relay CTR releases to close its back contact b, the pickup of relay BTR checks that the train has now moved into next track section in advance, that is, track section CT. This pickup circuit arrangement eliminates an incorrect nonoccupied indication by relay BTR if, due to an improper delivery fault in the communication system, receiver information from another wayside location is inadvertently delivered to the speed command comparison unit associated with relay BTR. This circuit is obviously not a complete or 100 percent cure of all faults but increases the fail-safe capacity of the system, in particular against errors due to communication system faults occurring from outside influences which result in improper time slot selector operation.

The arrangement of my invention also adds additional safety circuits in order to eliminate any error due to the improper delivery of speed command signals caused by the inadvcrtent incorrect operation of a time slot selector because of communication system faults of a type similar to that just described. As previously mentioned, when a track section is occupied, no speed command signal can be provided from the wayside receiver for transmission to the central station for delivery to the corresponding speed command comparison unit. Therefore, no check of what speed command signal is actually delivered to the rails by the corresponding wayside track transmitter at the entrance end of that section is possible under these conditions. For example, if track section BT is occupied, obviously receiver fl-fl is shunted and receives no track current signal. Accordingly, a track occupied indication is supplied to the central station. The speed command comparison unit at the central station thus receives no indication of the speed command signal delivered to the rails of sections AT and BT and no comparison is possible with the selected speed command signal transmitted from speed command generator SCGA. Thus the signal supplied from the wayside transmitter at location 1 into approach track section AT for delivery to an approaching train can not be checked and an inadvertent operation of time slot selector No. l at a wrong time in the scanning cycle would not be discovered. Under these conditions, of course, the signal supplied by transmitterfl-fl to the rails of section AT should be a restricted speed signal. If an improper operation of wayside selector No. 1 occurs, a less restrictive or proceed speed command intended for another location may also be delivered to location I transmitter apparatus.

In order to eliminate this possible hazard, I provide a break in the connection between the transmitter command line and the speed command memory unit at each location, this connection, of course, including the gate controlled by the associated time slot selector. This break in the connection is normally closed over front contacts of the advance section track relay at the central station. For example, for wayside location l, the connection from the transmitter command line to the gate controlled by time slot selector No. l, for delivering a speed command signal to the speed command memory unit of that location, is traced from the transmitter command line to terminal A and thence to the corresponding terminal A at the central station (shown at the left of FIG. 2) and over front contact c of track relay BTR to terminal B at the central station, thence to the corresponding terminal B at location No. l and the gate which, when enabled, completes the connection to the speed command memory unit at that location. Each other field location is provided with a similar pair of terminals which are matched at the central location. A direct line connection (not shown) is provided between each terminal at a wayside location and the similarly designated terminal at the central station of FIG. 2. These connections are in addition to the conventional communication system channels designated by the three lines across the bottom of the two figures.

When track section ET is occupied, this connection to the gate at location 1 is shifted to provide a direct connection from the restricted speed command signal source in speed command generator SCGA over back contact 0 or relay BTR to terminal B at the central station and thence by the direct connection to terminal B at location 1 and through the gate, when enabled, to the speed command memory unit. Thus whenever time slot selector No. l at the wayside location is actuated, whether correctly or through an inadvertent error in the communication system, to enable the associated gate, a restricted speed command signal is applied through this gate to the speed command memory at that location. No other speed command signal can be received under these conditions when track section BT is occupied by a train. Thus the transmission of a restricted speed command to an approaching train in section AT is assured.

I shall now briefly describe the overall operation of the system arrangement including my invention. It is assumed that no trains are moving through the stretch of track illustrated, at least in section BT, CT, and DT. The communication system is operating in its continuous cycling manner, sequentially scanning the locations and thus actuating sequence time slot selectors No. l, 2, 3, and so forth throughout all of the wayside and central station, repeating the scan cycle immediately upon completion of the preceding one. When the time slot selectors No. 1 are actuated, one at the wayside location and the other at the central station, each enables the associated gate units. Speed command generator SCGA at the central station then Eli transmits over the communication channel a speed command signal to the speed command memory unit at location 1. This is possible at this time since, with no train occupying the section, relay BTR is picked up and its front contact is closed to complete the circuit between terminals A and B over the direct wire connections involved. The speed command signal received selects, through the frequency shift modulation unit, a particular modulation pattern corresponding to the speed command desired. Wayside track transmitter fl-fl' supplies track current having this pattern to the rails of both sections AT and ET. The apparatus on any train approaching at this time through track section AT, being responsive thereto, receives the speed command signal, decodes the pattern, and controls the operation of the train in accordance with the speed signal received. The signal from transmitter fl-fl' is also received by wayside track receiver fl-fl' at location 2. This receiver unit prepares an indication signal for subsequent transmission to the central station, indicating both the nonoccupied status of track section BT and the actual speed command signal received.

As the communication system scanning cycle continues, time slot selectors No. 2 are next actuated. A speed command signal is then transmitted by generator SCGB to the speed command memory and frequency modulation units at wayside location 2 to effect the transmission of a track current having the frequenciesfZ-fi' modulated in the selected signal pattern through track sections BT and CT. This transmission of the speed command signal from the central station to the location is possible since front contact 6 of relay CTR is closed to complete the circuit between terminals C and D at the two locations. At the same time, an indication signal is transmitted by the receiver at location 2 over the receiver information channel to the speed comparison unit associated with safety unit VSPB. This received signal is compared with the speed command selection previously transmitted from speed command generator SCGA. lf a comparison between the two signals exists, energy is supplied to unit VSPB to hold relay BTR energized over its previously traced stick circuit. In other words, a nonoccupied track signal is supplied by this speed command comparison unit, which is actuated when time slot selector No. 2 is active, since a comparison exists between the transmitted and received speed command signals. Relay BTR then remains energized to indicate the nonoccupied condition of the track section. Time slot selectors No. 3 are next actuated and a speed command signal is transmitted from generator SCGC to the location 3 wayside track transmitter since front contact c of relay DTR is closed. At the same time, a train detection, speed signal is received from receiverf2-j2 at location 3 and is applied to the comparison unit associated with safety unit VSPC. lf proper comparison exists, between corresponding speed command signals, energy continues to be supplied to hold relay CTR picked up.

As a train moves through the stretch of track, it receives a speed command signal in each track section from the wayside transmitter located at the exit end of that section. For example, as the train traverses section AT, it receives a signal from transmitter flfl and while in section BT, from transmitter f2-f2'. The train carried apparatus is capable of responding to each set of audio frequencies used in the stem. When this train occupies section ET, the track current of frequency fl-fl is shunted away from receiverfl-fl' at location 2 by the shunt between the rails established by the wheels and axles of the train. When time slot selector No. 2 5 next actuated, no speed command signal is supplied to the comparison unit associated with unit VSPB since the corresponding wayside receiver has no current supplied thereto. This lack of speed signal at the central station, in effect a track section occupied indication, causes removal of energy release relay BTR to indicate the occupied track. The opening of front contact 0 of relay BTR breaks the direct connection between terminals A and B while, as previously discussed, the closing of back contact c applies a restricted speed signal directly to terminal B from speed command generator SCGA. While this track occupied condition holds, only a restricted speed signal is applied to the speed command memory unit at location 1 whenever time slot selector No. l is actuated. Thus even if an improper and untimely selection of location 1 results from a communication system fault, the restricted speed signal is still applied to track section AT for any following train, then approaching, which must stop short of the train already occupying section BT. Similar operation occurs as the leading train continues to advance through sections CT and DT through the operation of track relays CTR and DTR to sequentially release to indicate occupancy of these sections by the train. Although this arrangement requires additional line wires or channel connections between the central station and the various wayside locations, the added safety which it provides to the overall ATO system justifies the additional expense ofinstallation.

Once relay BTR has released so that its stick circuit is open at its own front contact a, it can not be reenergized until relay CTR releases to close its back contact b. That is, even if the comparison unit associated with safety unit VSPB provides an output to incorrectly indicate a nonoccupied condition of track section BT through some error of the communication system, relay BTR cannot be reenergized because its pickup circuit is open at back contact b of relay CTR. When relay CTR does release to indicate that the train has now occupied the advance section and a subsequent nonoccupied indication is applied to unit VSPB by its associated speed command com parison unit, the pickup circuit for relay BTR is then complete and this latter relay is reenergized to indicate the nonoccupied condition of that track section. These interconnections to provide this safety feature are within the central station wiring and relatively little additional expense, if any, is involved. However, by preventing the improper delivery of a nonoccupied track signal from incorrectly reenergizing relay BTR until relay CTR has released, the restricted speed command signal continues to be applied over back contact 0 of relay BTR and through terminals B to location l under this situation and this safety feature is continued.

Summarizing, the arrangement of my invention thus improves or adds to the safety of the basic ATO system. With these additions, the probability of proper fail-safe operation of the ATO system is increased even under the possibility of communication system faults which are known to be unavoidable with continuous operation. The arrangement assures the delivery of restricted speed commands to following trains in an approach tract section immediately behind that occupied by the preceding train. Further, the possibility of false nonoccupied track indications is reduced by including a check that the advance section has been occupied by the train before recording the nonoccupied condition of a track section. Thus, a train is not lost while it remains in a track section or is moving into the next section through the loss of track shunt or, more probably, through a system error in the delivery of track occupancy indications. Although some added installation costs result from this arrangement, the increase is justified by the greatly increased safety characteristics of the system. Overall then, an operable and efficient ATO system with increased safety characteristics results from the arrangement of my invention.

Although l have herein shown and described but one specific arrangement embodying the added circuits of my invention, it is to be understood that various modifications and changes may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a speed control system for trains moving over a stretch oftrack divided into sections at preselected wayside locations, each train being equipped for receiving and responding to speed command signals transmitted through the rails of said track, said system including a central control station within said stretch, the combination comprising,

a. a track transmitter at each wayside location coupled to said rails for transmitting a distinct speed command signal to control approaching trains and a corresponding signal for train detection into the advance section,

b. a track receiver at each wayside location coupled to said rails and responsive only to the detection signal transmitted by the track transmitter at the entrance end of the approach section for recording jointly a section nonoccupied indication and the corresponding speed command signal when a detection signal is received and a section occupied indication when the detection signal is absent,

c. a communication system between said central station and each wayside location connected for selectively transmitting speed commands and occupancy indications between said. station and said locations,

d. a speed command generator at said central location for each wayside location selectively connected to said communication system for transmitting to the corresponding wayside track transmitter a speed command selected in accordance with advance traffic conditions,

e. a speed command comparison unit at said central station for each wayside location selectively connected to said communication system for receiving the combined track occupancy and received speed command indication from the corresponding track receiver,

. each speed command comparison unit also cross connected to the speed command generator for the first wayside location in approach for comparing the speed command transmitted to the approach location track transmitter with that received by the corresponding track receiver,

f. a safety protection unit at said central station for each track section connected for receiving the occupancy indication from the speed command comparison unit associated with the exit end of the corresponding track section and interconnected with other safety protection units for establishing the advance traffic condition which determines the allowable speed command for a train in the approach section,

I. each speed command comparison unit delivering a nonoccupied indication for the approach track section to the associated safety protection unit when and only when the received speed command indication agrees with the speed command transmitted by the associated speed command generator to the entrance end track transmitter,

g. a track relay associated with each safety protection unit and controlled by the associated speed command comparison unit to a first position or a second position as a section nonoccupied or occupied indication, respectively, is supplied to the associated safety protection unit,

h. a first circuit at said central station for each track section including a first position contact of the corresponding track relay and interposed in the connections, between said communication system and the entrance end track transmitter, by which the selected speed commands are delivered to that track transmitter, and

. an alternate circuit for each track section including a second position contact of the corresponding track relay and connected for supplying only a restricted speed command direct to the entrance end track transmitter from the associated speed command generator so that a proceed speed command can not be supplied to a following train in the adjoining approach track section.

2. A speed control system as claimed in claim 1, which further includes,

a. a stick circuit for each track relay energized by the associated speed command comparison unit while a nonoccupied track indication is continuously recorded, and

b. a pickup circuit for each track relay also energized by the associated speed command comparison unit and including a second position contact of the track relay associated with the advance track section, whereby a nonoccupied indication for the associated section after being occupied by a train can not he recorded by a track relay until an occupied indication for the advance track section is recorded.

3. A speed control system for trains traversing a stretch of railroad track which is divided into sections at preset locations, said trains being provided with apparatus responsive to speed command signals applied to the track rails for controlling train speed, said system including a central apparatus station for supervisory control and having associated therewith a communication system linking said central station and all said preset locations, comprising in combination,

a. a speed command signal circuit means for each track section for providing through said rails selected speed command signals to trains traversing the section,

I. each signal circuit means including a source of signal energy coupled to the rails at the exit end of the corresponding section and also connected to said communication system for receiving said selected speed commands from said central station,

b. a detector track circuit means for each track section coupled to the rails at the exit end of the corresponding section for determining the presence or absence of a train in that section and connected to said communication system for transmitting section occupancy indications to said central station,

I. each detector circuit means having a common source of energy with the speed command signal circuit means for the adjoining approach track section,

2. each nonoccupied section indication transmitted by a detector track circuit means including a supplemental indication of the speed command signal received from the source common with the adjacent speed command signal circuit means,

. a speed command generator at said central station for each track section connected to said communication system for selectively transmitting a selected speed command signal to control the speed command signal source for the corresponding section,

d. a speed command comparison unit at said central station for each track section connected for receiving the section occupancy indications transmitted by the corresponding detector circuit means and when transmitted the supplemental received speed command signal indication,

. each comparison unit controlled by the approach section speed command generator for comparing the selected speed command signal with the received speed command indication,

e. a safety means at said central station for each track section including a track relay operable to a first and a second position to record a nonoccupied and an occupied indication, respectively, for the corresponding track sec tion,

1. each safety means controlled by the associated track relay and by the safety means for advance track sections in accordance with their recorded section occupancy conditions for establishing the advance traffic condition which determines the allowable speed command signal for a train in the adjoining approach track section,

2. each safety means controlling the speed command generator for the adjoining approach section for selecting the transmitted speed command signal in accordance with the advance traffic condition,

each speed command comparison unit coupled to the track relay in the associated safety means for operating that relay to its first position only when a section nonoccupied indication is received from the associated detector circuit means and the supplemental speed command signal indication received agrees with the selected speed command transmitted by the speed command generator for the approach track section,

. a first circuit associated with each safety means including a first position contact of the associated track relay and connected for supplying the selected speed command each track relay is provided with,

a. a stick circuit means controlled by the associated speed command comparison unit for retaining the relay in its first position while a nonoccupied track indication is continuously received, and

. a pickup circuit means including a second position contact ofthe track relay for the adjoining advance track section and controlled by the associated speed command comparison unit for restoring the relay to its first position after an occupied track indication has been recorded only when an occupied track indication has subsequently been recorded by said advance section track relay and a nonoccupied track indication is received from the corresponding detector track circuit means. 

1. In a speed control system for trains moving over a stretch of track divided into sections at preselected wayside locations, each train being equipped for receiving and responding to speed command signals transmitted through the rails of said track, said system including a central control station within said stretch, the combination comprising, a. a track transmitter at each wayside location coupled to said rails for transmitting a distinct speed command signal to control approaching trains and a corresponding signal for train detection into the advance section, b. a track receiver at each wayside location coupled to said rails and responsive only to the detection signal transmitted by the track transmitter at the entrance end of the approach section for recording jointly a section nonoccupied indication and the corresponding speed command signal when a detection signal is received and a section occupied indication when the detection signal is absent, c. a communication system between said central station and each wayside location connected for selectively transmitting speed commands and occupancy indications between said station and said locations, d. a speed command generator at said central location for each wayside location selectively connected to said communication system for transmitting to the corresponding wayside track transmitter a speed command selected in accordance with advance traffic conditions, e. a speed command comparison unit at said central station for each wayside location selectively connected to said communication system for receiving the combined track occupancy and received speed command indication from the corresponding track receiver,
 1. each speed command comparison unit also cross connected to the speed command generator for the first wayside location in aPproach for comparing the speed command transmitted to the approach location track transmitter with that received by the corresponding track receiver, f. a safety protection unit at said central station for each track section connected for receiving the occupancy indication from the speed command comparison unit associated with the exit end of the corresponding track section and interconnected with other safety protection units for establishing the advance traffic condition which determines the allowable speed command for a train in the approach section,
 1. each speed command comparison unit delivering a nonoccupied indication for the approach track section to the associated safety protection unit when and only when the received speed command indication agrees with the speed command transmitted by the associated speed command generator to the entrance end track transmitter, g. a track relay associated with each safety protection unit and controlled by the associated speed command comparison unit to a first position or a second position as a section nonoccupied or occupied indication, respectively, is supplied to the associated safety protection unit, h. a first circuit at said central station for each track section including a first position contact of the corresponding track relay and interposed in the connections, between said communication system and the entrance end track transmitter, by which the selected speed commands are delivered to that track transmitter, and i. an alternate circuit for each track section including a second position contact of the corresponding track relay and connected for supplying only a restricted speed command direct to the entrance end track transmitter from the associated speed command generator so that a proceed speed command can not be supplied to a following train in the adjoining approach track section.
 2. each safety means controlling the speed command generator for the adjoining approach section for selecting the transmitted speed command signal in accordance with the advance traffic condition, f. each speed command comparison unit coupled to the track relay in the associated safety means for operating that relay to its first position only when a section nonoccupied indication is received from the associated detector circuit means and the supplemental speed command signal indication received agrees with the selected speed command transmitted by the speed command generator for the approach track section, g. a first circuit associated with each safety means including a first position contact of the associated track relay and connected for supplying the selected speed command signal transmitted by the speed command generator for the adjoining approach track section to the corresponding speed command signal source, and h. a second circuit associated with each safety means including a second position contact of the associated track relay connected for supplying to the approach section speed command signal source only a restricted speed command signal to be provided to a train occupying the adjoining approach track section when another train is occupying the corresponding track section.
 2. each nonoccupied section indication transmitted by a detector track circuit means including a supplemental indication of the speed command signal received from the source common with the adjacent speed command signal circuit means, c. a speed command generator at said central station for each track section connected to said communication system for selectively transmitting a selected speed command signal to control the speed command signal source for the corresponding section, d. a speed command comparison unit at said central station for each track section connected for receiving the section occupancy indications transmitted by the corresponding detector circuit means and when transmitted the supplemental received speed command signal indication,
 2. A speed control system as claimed in claim 1, which further includes, a. a stick circuit for each track relay energized by the associated speed command comparison unit while a nonoccupied track indication is continuously recorded, and b. a pickup circuit for each track relay also energized by the associated speed command comparison unit and including a second position contact of the track relay associated with the advance track section, whereby a nonoccupied indication for the associated section after being occupied by a train can not be recorded by a track relay until an occupied indication for the advance track section is recorded.
 3. A speed control system for trains traversing a stretch of railroad track which is divided into sections at preset locations, said trains being provided with apparatus responsive to speed command signals applied to the track rails for controlling train speed, said system including a central apparatus station for supervisory control and having associated therewith a communication system linking said central station and all said preset locations, comprising in combination, a. a speed command signal circuit means for each track section for providing through said rails selected speed command signals to trains traversing the section,
 4. A speed control system as claimed in claim 3 in which each track relay is provided with, a. a stick circuit means controlled by the associated speed command comparison unit for retaining the relay in its first position while a nonoccupied track indication is continuously received, and b. a pickup circuit means including a second position contact of the track relay for the adjoining advance track section and controlled by the associated speed command comparison unit for restoring the relay to its first position after an occupied track indication has been recorded only when an occupied track indication has subsequently been recorded by said advance section track relay and a nonoccupied track indication is received from the corresponding detector track circuit means. 